Excimer laser chambers have long been employed to generate gas discharge laser light for integrated circuit lithography. Generally speaking, an excimer laser chamber may include a housing within which there exist a set of spaced-apart electrodes, a circulation system for circulating an appropriate laser gas (typically under pressure) between the electrodes, and pulsing circuitry for pulsing the electrodes. The laser gas may comprise a mixture of suitable gases, including without limitation fluorine, krypton, and neon, for example.
For ease of referencing and not by way of limitation, the upper electrode may be thought of generally as the cathode and maybe rapidly pulsed with negative electrical signal pulses while the lower electrode, which may be thought of as the anode, may be grounded. This is a typical configuration and variations may exist and thus no limitation is intended by this example.
The pulses across the electrodes cause electrical discharge in the spatial region between the electrodes. This electrical discharge excites the laser gas to produce pulses of laser light for photolithography purposes, as is well known to those familiar with laser-based photolithography.
For background reading, U.S. Pat. No. 6,466,602B1 and U.S. Pat. No. 7,301,980B2 (both incorporated herein by reference) describe some example excimer laser chambers and components thereof.
As integrated circuit features become smaller and smaller, it is increasingly important to maintain the quality of the output laser light for photolithography purposes during production. This is because variations in the output laser light result in inconsistent exposure of the photoresist from die to die and/or from wafer to wafer. Since the electrical discharges between the electrodes erode the electrodes over time, it is important to design electrodes for longevity (a metric for which may be mean time between service or MTBS) as well as for consistent output light quality over the lifetime of the electrodes.
The present invention relates to improved designs for electrodes for use in excimer laser chambers.